Hi, i was wondering if a 10' jon boat is to small to add a small casting deck on. Also what is the biggest outboard i could put on?

Too small.

5 h.p.

Agree 100 percent!

I also have a 10' jon and did put in a casting deck. The decking added weight, made the boat sit lower in the water and therefore a little more stable while we're sitting. standing on it is quite tippy, but if you're careful and only use it on small bodies of water you could make it work. I had the original intention of just rowing and putting around, but as usual I took it too far.  Here are a few pictures.

http://i639.photobucket.com/albums/uu119/roberthull3939/10ftjon001-1.jpg

http://i639.photobucket.com/albums/uu119/roberthull3939/10ftjon002.jpg

http://i639.photobucket.com/albums/uu119/roberthull3939/10ftjon003.jpg

Greatoutdoors nice looking rig. I have seen decks on 10' but they were low I think it would be tippy JMHO

Greatoutdoors nice looking rig. I have seen decks on 10' but they were low I think it would be tippy JMHO

Thanks, just finished it up and got it out. It is tippy when standing on the front deck, but when we're both sitting it isn't that bad. It's no Skeeter, but it'll catch me more fish than walking the banks. I wouldn't advise against doing it, because 10 footers are tippy to begin with, I just recommend that you be cautious while on the water.